JP3540715B2 - Underwater propagation signal receiver - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an underwater propagation signal receiving apparatus for receiving a signal transmitted from underground at a predetermined depth and reaching the ground by underwater transmission, for example.
[0002]
[Prior art]
Conventionally, a device that receives a signal transmitted from a signal source existing underground at a predetermined depth and transmitted by underwater transmission has been configured, for example, as shown in FIG. In FIG. 4, reference numerals 1a and 1b denote input terminals of a signal input unit, which are provided at reception points on the ground.
[0003]
The input signals input from the input terminals 1a and 1b are filtered only in a predetermined frequency band by the narrow band filter 2a, amplified by the amplifier 3a, and further filtered only in the predetermined frequency band by the narrow band filter 2b. And is amplified by the amplifier 3b.
[0004]
Reference numeral 4 denotes a carrier detector for detecting a signal having a level exceeding a reference threshold from the output signal of the amplifier 3b. The signal detected by the carrier detector 4 is converted into a digital signal by a digital signal processing circuit 5.
[0005]
The configuration shown in FIG. 4 is a method usually employed in the line of a telecommunications carrier, and the provision of the narrow-band filters 2a and 2b as early as possible eliminates unnecessary frequency components as early as possible, and This is for preventing the occurrence of modulation or the like and for amplifying the intended reception frequency with emphasis.
[0006]
In the case of a line of a telecommunications carrier, the reception input level is at least about -43 dBm, and it is sufficient that the carrier can be detected at this level, so that the amplification of the receiver is about 60 dB. Further, even if the reception dead level is set to, for example, -48 dBm, the noise level of the line is sufficiently lower than that, so that the noise does not influence the dead level. These advantages are possible because carriers always provide good quality circuits with low loss and low noise.
[0007]
[Problems to be solved by the invention]
However, in the case of transmitting operation information of a machine that operates underwater about 80 m underground, such as an excavator for foundation work of a building, from the underground and receives it on the ground, it can be received by the conventional technology as shown in FIG. It is up to about 15m at the depth of the excavator. A signal transmitted by an excavator operating at a depth of 40 m or deeper has a large attenuation, and it is not practical to receive a signal without an amplification of about 140 dB or more.
[0008]
Here, if a high amplification degree of 140 dB or more is to be obtained as a whole by a method of arranging a narrow-band filter in the preceding stage as in the conventional apparatus of FIG. . This is because the phase shift is large at a frequency near the center of the narrow band filter. That is, even if the stray capacitance is very small, and even if the inductance of the conductor of the power supply or the ground circuit system is small, oscillation is caused by a synergistic effect of high amplification and phase displacement.
[0009]
In general, even if there is no external noise, there is thermal noise and shot noise generated by the resistance of the input circuit of the receiver. Is considered impossible.
[0010]
Further, the conventional carrier detection method is, for example, a determination as to whether or not a signal is present as in the case of the carrier detector 4 in FIG. 4, and is based on whether or not the detected signal has a level exceeding a reference threshold value. Deciding. For this reason, the judgment becomes ambiguous if the input signal is not sufficiently higher than the noise level. That is, carrier detection of a signal buried in noise is impossible with the conventional technology.
[0011]
Furthermore, when the conventional technology is introduced, when the work is started with the excavator, there is a transmitter at 0 m underground, and the reception level is as high as + several tens dBm. On the other hand, the reception level on the ground of a signal transmitted from 40 m or less underground is equal to or less than -140 dBm, and is buried in noise generated by the resistance of the input circuit and noise mixed into the input circuit.
[0012]
If such a level difference of the input signal is directly input to the detector, it is difficult to determine whether the signal is present or not. This is usually dealt with by an automatic gain adjustment circuit, but the automatic gain adjustment function of a weak signal buried in the noise level does not operate.
[0013]
The present invention has been made in view of the above points, and an object thereof is to obtain a sufficient amplification degree without causing oscillation, to enable detection of a signal buried in noise, and to reduce a level difference between input signals. An object of the present invention is to provide an underwater propagation signal receiving device that can reliably identify the presence or absence of a signal even if the signal is large.
[0014]
[Means for Solving the Problems]
The underwater propagation signal receiving apparatus of the present invention for solving the above-mentioned problems is a receiving apparatus for receiving an underwater propagation signal transmitted by underwater transmission, wherein a signal input unit is provided with excessive input protection means, and the excessive input protection means is provided. A first amplifying means having a frequency signal higher than a set frequency and having an amplitude compression function, and a second amplifier having a frequency signal lower than the set frequency and having an amplitude compression function. Means are provided in series, and a third amplification means having an amplitude compression function and selecting a desired frequency signal is provided on the output side of the series body of the first and second amplification means, and the third amplification means is provided. On the output side of the means, a detection means for outputting a signal which is higher than a predetermined level and lasts for a predetermined time or more among the output signals of the third amplifying means is provided,
Each of the amplitude compressing functions of the first, second and third amplifying means is characterized in that it has a compression characteristic substantially symmetric with respect to the polarity of the signal amplitude.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals. The input signals input from the input terminals 1a and 1b are supplied to the high-pass filter 11 via the excessive input protection circuit 10, and only the frequency signals higher than the set frequency pass. After the output signal of the high-pass filter 11 is amplified by the amplifier 3c, the amplitude is limited by the amplitude limiting circuit 12a.
[0016]
The output signal of the amplitude limiting circuit 12a is supplied to the low-pass filter 13, and only the frequency signal equal to or lower than the set frequency passes. After the output signal of the low-pass filter 13 is amplified by the amplifier 3d, the amplitude is limited by the amplitude limiting circuit 12b.
[0017]
After the output signal of the amplitude limiting circuit 12b is amplified by the amplifier 3e, the amplitude is limited by the amplitude limiting circuit 12c. The output signal of the amplitude limiting circuit 12c is supplied to a selection amplifier 14, and only a desired frequency signal is selectively amplified.
[0018]
The output signal of the selection amplifier 14 is compared with a reference threshold value in a detector 15 and a signal having a level higher than the threshold value is extracted. The output signal of the detector 15 is determined by the carrier determiner 16 as to whether or not its duration is equal to or longer than a set time, and a signal having continued for the set time or longer is output as a target reception signal.
[0019]
The output signal of the carrier determination 16 is converted by the digital signal processing circuit 5 into a digital signal.
[0020]
FIG. 2 shows an embodiment in which the high-pass filter 11, the low-pass filter 13 and the amplifiers 3c to 3e are provided with an amplitude compression circuit. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.
[0021]
Input signals input from the input terminals 1a and 1b are supplied to a high-pass filter amplifier 20a with an amplitude compression circuit via an excessive input protection circuit 10. The high-pass filter amplifier 20a with an amplitude compression circuit passes and amplifies a signal having a frequency equal to or higher than a set frequency, and performs amplitude compression.
[0022]
The output signal of the high-pass filter 20a with the amplitude compression circuit is supplied to the low-pass filter 21a with the amplitude compression circuit. The low-pass filter amplifier 21a with an amplitude compression circuit passes and amplifies a frequency signal equal to or lower than a set frequency and performs amplitude compression.
[0023]
The output signal of the low-pass filter with amplitude compression circuit 21a is supplied to the high-pass filter with amplitude compression circuit 20b. The high-pass filter amplifier 20b with an amplitude compression circuit passes and amplifies a frequency signal equal to or higher than a set frequency and performs amplitude compression.
[0024]
The output signal of the high-pass filter 20b with the amplitude compression circuit is supplied to the low-pass filter 21b with the amplitude compression circuit. The low-pass filter amplifier 21b with an amplitude compression circuit passes and amplifies a frequency signal equal to or lower than a set frequency and performs amplitude compression.
[0025]
The output signal of the low-pass filter with amplitude compression circuit 21b is supplied to the selection amplifiers 14a and 14b. Selection amplifier 14a, 14b are respectively selected amplifies only a desired frequency signal F _a, F _Z, respectively output detector 15a, to 15b. The detectors 15a and 15b compare each input signal with a reference threshold and extract a signal having a level higher than the threshold. The output signals of the detectors 15a and 15b are determined by the carrier determiner 16 as to whether or not the duration is longer than a set time, and a signal that has continued for the set time or longer is output as a target reception signal.
[0026]
The output signal of the carrier determiner 16 is converted by the digital signal processing circuit 5 into a digital signal.
[0027]
1 and 2, the amplitude compression functions of the amplitude limiting circuits 12a to 12c, the high-pass filter amplifiers 20a and 20b with an amplitude compression circuit, and the low-pass filter amplifiers 21a and 21b with an amplitude compression circuit are as follows. As shown in FIG. 3, it has a compression characteristic substantially symmetric with respect to the polarity of the input signal amplitude.
[0028]
This amplitude compression circuit (amplitude limiting circuit) is basically a circuit for limiting the amplitude in a form in which two diodes are connected in parallel in opposite directions. The forward saturation voltage is about 0.3 V for a germanium diode and about 0.7 V for a silicon diode.
[0029]
For example, if an amplitude compression circuit (amplitude limiting circuit) is constituted only by germanium diodes, no self-oscillation is likely to occur internally at any point on the circuit of the cascade amplification stage because the peak does not exceed ± 0.3 V. The gist of the present invention is to incorporate this amplitude compression circuit (amplitude limiting circuit) in all amplifiers including the first-stage amplifier that handles minute levels. It should be noted that there is no amplitude compression effect on a signal having a level sufficiently lower than the saturation voltage, so that a corresponding gain can be obtained.
[0030]
In addition, since only the high-pass filter and low-pass filter are used without using the narrow-band filter in the previous stage, there is no significant displacement of the phase in each stage. Hard to get up.
[0031]
The role of the selection amplifiers 14, 14a, and 14b is to select only the intended reception signal. The input of the selection amplifier includes a reception input signal, external noise, noise generated by the resistance of the input circuit, and interstage noise. The generated noise and the like are mixed to form a signal subjected to amplitude compression.
[0032]
The higher the selectivity of the selection amplifiers 14, 14a, 14b, the easier it is to extract a signal buried in noise. However, if the degree of amplification is too high, the output amplitude will fluctuate almost to the full power supply, and there is a possibility that the oscillation will occur due to internal coupling. Therefore, it is necessary to appropriately adjust the amplitude.
[0033]
If a silicon diode amplitude compressor is used immediately before the selection amplifiers 14, 14a and 14b, the required detection input level can be obtained without increasing the amplification of the selection amplifier too much, thereby preventing oscillation.
[0034]
The detectors 15, 15a, and 15b may be collapsing line detectors, but a coherent detector can expect stable reception even if the signal-to-noise ratio further decreases. The frequency components of the noise are mixed and the noise frequency may cross the signal frequency to be received.
[0035]
This is a phenomenon that can occur stochastically. Usually, the time that remains in the frequency range, that is, the time that is output from the selection amplifiers 14, 14a, and 14b is within a certain time, or the empirical waveform 3 It is confirmed that it is less than the cycle.
[0036]
Therefore, in the present invention, a threshold value of the level is set at the time of carrier detection, a signal that is equal to or higher than the threshold value is set as the first condition of carrier detection, and the duration is also determined (carrier determination unit 16). It is configured as follows. By taking measures such as counting the time duration of the signal equal to or longer than the threshold value with a time pulse or delaying the duration with an integrating circuit, it becomes sufficiently practical.
[0037]
However, since the time required for this determination is wasted and the transmission speed must be reduced, the operation is performed at about 50 to 100 bps for transmission in the audible frequency band.
[0038]
Further, according to the circuit system of the present invention, even if there is a difference of about 200 dB in the level of the input signal due to a difference in the depth of the underground, for example, it can be protected by the excessive input protection circuit provided in the input stage of the receiving device, Can be well adapted.
[0039]
On the other hand, a normal automatic gain adjusting device cannot adapt to a weak input whose signal level is buried in noise.
[0040]
Since the amplitude compression circuit (amplitude limiting circuit) uses an amplitude compression circuit whose compression characteristic with respect to the polarity of the input signal amplitude is substantially symmetrical, it is necessary to suppress generation of odd-order harmonics internally. Can be.
[0041]
As more specific embodiment of the present invention, the setting of the selected amplifier 14a Figure 2, 14b of the set frequency F _a, a F _Z, for example, a frequency modulation scheme F _a = 2100H _Z, the F _Z = 1300H _Z I do.
[0042]
In this case was set to F _Z = 1300H _Z, band of the high pass filter (20a, 20b) is set to more than 1300h _Z, also since the F _a = 2100H _Z, low-pass filter (21a, band 21b) is set below 2100H _Z.
[0043]
And when the communication speed with the 100 bps, minimum duration of the F _a or F _Z is so 10 ms, setting the signal duration determination time of the carrier detector 16 to about 3 ms. Also when the communication speed with 50bps may minimum duration of F _a or F _Z is 20ms So setting the signal duration determination time of the carrier detector 16 to about 5～7Ms. As the communication speed decreases, an improvement in the bit error rate can be expected.
[0044]
In the above-described embodiment, the low-pass filtering is performed after the high-pass filtering is performed. However, the invention is not limited thereto, and the high-pass filtering may be performed after the low-pass filtering is performed. .
[0045]
Further, the first to third amplifying means and detecting means constituting the present invention are not limited to those of the above-described embodiment, but may be constituted by other circuits having the same functions.
[0046]
【The invention's effect】
As described above, according to the present invention, since the first to third amplifying units have an amplitude compression function, internal self-oscillation does not occur, and a sufficient amplification degree can be obtained.
[0047]
Further, since a narrow-band filter is not used in the preceding stage of the device, there is no significant displacement of the phase in each stage, so that internal self-oscillation does not occur and a sufficient amplification degree can be obtained.
[0048]
In addition, since the detection means is configured to output a signal having a predetermined level or more and lasting for a predetermined time or more, of the signals selected from the desired frequency signal, the detection means also detects a weak signal buried in noise. be able to.
[0049]
Further, since the excessive input protection means is provided, it is possible to sufficiently detect the presence / absence of an input signal having a large level difference. Particularly, for example, the present invention is applied to a field in which a signal having a very large input level difference is received such that the transmitter moves from a depth of 0 m underground to a depth of 40 m or less (for example, 80 m) by the operation of an excavator, and a great effect is obtained. .
[0050]
Further, by configuring each amplitude compression function of the first to third amplification means to have a compression characteristic substantially symmetrical with respect to the polarity of the signal amplitude, odd-order harmonics are generated internally. Can be suppressed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an embodiment of the present invention.
FIG. 2 is a block diagram showing another embodiment of the present invention.
FIG. 3 is a characteristic diagram showing input / output characteristics of the amplitude compression function of the present invention.
FIG. 4 is a block diagram showing an example of a conventional underwater propagation signal receiving device.
[Explanation of symbols]
1a, 1b Input terminals 3a to 3e Amplifier 5 Digital signal processing circuit 10 Excessive input protection circuit 11 High frequency filters 12a to 12c Amplitude limiting circuit 13 Low frequency filters 14, 14a, 14b Selection amplifiers 15, 15a, 15b Detector 16 Carrier determiners 20a, 20b High-pass filter amplifiers 21a, 21b with amplitude compression circuit Low-pass filter amplifier with amplitude compression circuit

Claims (2)

In a receiving device that receives an underwater propagation signal transmitted by underwater transmission,
Provide excessive input protection means in the signal input section,
On the output side of the excessive input protection means, a first amplifying means having a frequency signal higher than a set frequency and having an amplitude compression function, and a frequency signal having a frequency lower than the set frequency and having an amplitude compression function are provided. Provided in series with the second amplification means,
On the output side of the series body of the first and second amplifying means, there is provided a third amplifying means having an amplitude compression function and selecting a desired frequency signal;
On the output side of the third amplifying means, there is provided a detecting means for outputting a signal which is higher than a predetermined level and lasts for a predetermined time or more among the output signals of the third amplifying means. Underwater propagation signal receiving device. 2. The underwater propagation according to claim 1, wherein each amplitude compression function of the first, second and third amplifying means has a compression characteristic substantially symmetric with respect to the polarity of the signal amplitude. Signal receiving device.

Images